THE INFLUENCE oF LIGHT ON ORGANS 427 
time 386 pounds in weight. From this observation Pleasan- 
ton concluded that violet light is favorable to the growth of 
pigs. General Pleasanton’s book is printed in blue type, and 
gives an explanation of all natural phenomena, from love 
down to the activity of a volcano. 
Emil Young made a series of experiments on the influ- 
ence of colored light on development. He concluded that 
violet light hastens to a certain degree the development of 
frogs’ eggs, and the growth of embryos, while green light is 
fatal to or greatly retards development. Young’s results are 
incomprehensible. The larve of frogs develop naturally in 
daylight, and the latter contains more green light than light 
which has passed through a green screen, and should accord- 
ing to Young be fatal. We might, perhaps, assume that 
some other light counteracts the effect of the green light 
sufficiently to do away with this fatal effect. From Young’s 
experiments, however, this does not seem to be the case. It 
is quite possible that other conditions (such as the develop- 
ment of micro-organisms) affected the results of Young’s 
experiments, which lasted through several weeks. 
Driesch used monochromatic light and carried out the 
same experiments as Young on freshly fertilized eggs of 
Rana, Echinus, and Planorbis, and found, in all cases, that 
light “has no influence on the segmentation or the forma- 
tion of organs; under otherwise similar conditions these 
phenomena occur with the same velocity in darkness, in 
white, in green, in violet, or in other lights.” 
In my experiments on heteromorphosis in Naples, I 
observed that the polyps of Eudendrium racemosum are 
positively heliotropic, and that the number of polyps which 
develop is apparently dependent on the intensity of the light. 
It seemed that fewer polyps were developed in weak light 
than in strong light. This accidental observation led me to 
study the influence of light on the development of organs 
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